1. Field of the Invention
The subject invention relates to an epicardial implantable screw-in lead, and more particularly, to an epicardial pacing lead for left ventricular placement to effect bi-ventricular pacing of the heart.
2. Background of the Related Art
Implantable cardiac stimulation leads, including endocardial leads, are well known in the art. In general, these devices have an elongated flexible body with an electrode at one end for contacting cardiac tissue and a connector at the other end for mating with an automated stimulation device, namely a pacemaker.
Epicardial implantable pacing leads currently in use are amenable to flexible placement outside the heart, i.e., the left ventricle easily can be reached from the outside. However, the placement of epicardial leads into the myocardium often requires open heart surgery. Another disadvantage of placing leads epicardially is the increased pacing threshold caused by the fatty tissue layer outside the myocardium. Such increased threshold reduces the battery life of the pacemaker, creating the need for more frequent replacement of the battery or the pacemaker itself.
Pacing threshold is lowered when leads are placed endocardially. Another advantage of such placement of the leads, particularly when used in the coronary sinus or left ventricle for bi-ventricular pacing (resynchronization), is that it does not require open heart surgery. A particularly useful coronary sinus lead is disclosed in U.S. Patent Application Publication US 2003/0023295. However, the anatomy of the coronary sinus makes endocardial placement of the leads very difficult. In addition, endocardial left ventricular placement (transseptal approach from the right atrium) can be dangerous for patients, since any blood that arises could go directly into the blood circulation of the brain. Furthermore, transseptal approach requires a hole to be punctured into the septum to reach the left ventricle towards the left atrium. This could cause severe trauma to the patient.
When an endocardial lead has been implanted in the heart, either by active or passive fixation, it has been determined that the cardiac tissue at the site of implantation will react favorably to the lead in the presence of a therapeutic drug, for example, a steroid. Consequently, cardiac leads have been designed with means for delivering a therapeutic drug to the cardiac tissue at the implantation site. A particularly useful drug delivery device is disclosed in U.S. Patent Application Publication US 2003/0093138, the disclosure of which is incorporated by reference into the subject application. This device includes an insulating tube 26 that is formed from a compound that includes an elastomeric material and a therapeutic drug. In use, suitable drugs such as steroids elute from the elastomer over time, having a desirable effect on surrounding cardiac tissue. A distal end of the lead body is provided with a plurality of flexible tines to keep the lead tip firmly anchored within the cardiac tissue.
An example of a myocardial pacing lead is disclosed in U.S. Pat. No. 5,300,107, wherein an electrode 9 and a portion of the lead body penetrate the epicardium for direct stimulation of the myocardium. The lead includes two sets of opposing tines 3 and 7, the first row of tines 3 anchoring on the inside wall of the epicardium, and the second row of tines 7 preventing excessive penetration into the myocardium, thereby maintaining the electrode 9 in contact with the myocardium.
Another type of pacing lead is disclosed in U.S. Pat. No. 4,357,946, in which an epicardial pacing lead stylet is used to control a helical fixation screw which is rotated to engage the epicardial tissue of the heart. The stylet 30 is threaded through the lead, which is formed of a multifilar insulated coiled conductor, and configured such that a wedged tip 30b of the stylet 30 engages a complex gear set 50. The wedged tip 30b rotates the gear set 50, which drives the helical fixation screw 42 into the epicardial tissue. At fixation, a ring electrode 38 rests against epicardial tissue, the electrode being secured to the pacing site by the helical fixation screw 42. In the '946 patent, electrical stimulation is applied exclusively through the ring electrode 38; no electrical stimulation is effected through the helical fixation screw itself. Moreover, control of the screw is effected through a complex gear arrangement, and further requires a rotatable stylet to be internally threaded through the coiled conductor of the lead to transmit torque to the gears.
It would be beneficial to provide an epicardial screw-in lead that overcomes the deficiencies of the prior art. More particularly, it would be beneficial to provide an epicardial screw-in lead in which electrical stimulation is incorporated into the lead's fixation mechanism. Moreover, control of the screw preferably is provided in a simplified arrangement, while permitting the stylet to be positioned outside the lead.